The use of human drug discrimination studies in medication development.
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Discrimination, Psychological↗
Biomedical subjects
C E Johanson
Publications and source records attributed to C E Johanson.
Chloride efflux from isolated choroid plexus.
Chloride efflux was analyzed in adult rat lateral ventricle choroid plexus (LVCP) incubated in artificial CSF (aCSF) at 37 degrees C. Following steady-state loading of 36Cl in LVCP, the tracer release from plexus to aCSF was quantified by the efflux coefficient (k, s-1), equal to ln 2/t/2. Cl efflux could be described by a 2-component model, with a t/2 for the 'fast' component matching well that for [3H]sucrose (extracellular marker) and a slower, drug-inhibitable component of 36Cl release thought to reflect cellular washout. The cellular Cl efflux was more than twice as fast as 37 degrees C than at 15 degrees C. There was progressively more rapid efflux (k) of 36Cl from cells as the aCSF was altered over a range of several pH values from 6.7 (k = 0.026 s-1) to 8.2 (0.070 s-1). CSF medium anion replacement (isethionate and HEPES for Cl and HCO3, respectively) reduced the k for 36Cl by 57%. Acetazolamide (0.1 mM) and other Cl transport inhibitors (disulfonic stilbenes and loop diuretic) reduced Cl efflux by 35-55%. Acetazolamide inhibited Cl release from LVCP into aCSF whether the latter contained Cl and HCO3, or not. Overall, the findings suggest that Cl extrusion from choroid plexus is by way of an anion exchanger and via channels.
Acetazolamide↗
Response of infant and adult rat choroid plexus potassium transporters to increased extracellular potassium.
The choroid plexus (CP) has an important role in regulating ion concentrations in the cerebrospinal fluid (CSF). Maintenance of potassium concentration [( K]) in brain extracellular fluids lower than in serum is critical to proper neuronal function. We studied K (86Rb) transport by the isolated, lateral CP from infant and mature rats to determine the nature and development of CSF [K] regulation. Comparison of transport characteristics in media with 3-11 mM [K] showed that the adult CP increased uptake in a stepwise fashion with each 2 mM increase in [K], up to a 90% increase with 9 mM [K] over control (3 mM [K]). In contrast, 3-day CP increased uptake in 5 mM, but could not increase K uptake further with higher [K]. One-week tissues showed an intermediate response. Kinetic analysis of the ouabain-inhibitable component suggested that the immature tissues may express a different isoform of the catalytic (alpha) subunit of the Na,K-ATPase. These data may explain the previously established inability of neonatal rats to regulate CSF [K] when serum [K] is elevated, and they indicate that active K transport by the CP cells plays an integral role in CSF [K] regulation.
Aging↗
Potassium cotransport with sodium and chloride in the choroid plexus.
The effects of loop diuretics and ion substitution on the 2-min uptake of K (86Rb as marker) were analyzed to obtain evidence for K cotransport with Na and Cl in the choroid plexus epithelium. The isolated plexuses, which were excised from lateral ventricles of adult rats, were bathed in artificial cerebrospinal fluid (aCSF). At concentrations of 10(-6) to 10(-4) M, the specific cotransport inhibitors, bumetanide and piretanide, suppressed uptake of K in a dose-dependent manner. Ouabain-insensitive K uptake was stimulated by preincubating the choroid plexus in aCSF very low in [Na] and [K], then incubating it in much higher concentrations of these cations; bumetanide (10(-4)M) blocked this stimulated uptake by 52%. Moreover, tissue preincubation in Na- or Cl-free medium, followed by incubation with normal concentrations of both ions, stimulated the ouabain-insensitive uptake of K from 15 (baseline) to 35 nmol/mg dry weight. This stimulation of K transport depended on the simultaneous presence of both Na and Cl in aCSF, and replacing either ion alone did not stimulate the ouabain-insensitive K uptake. Collectively, these findings, together with those from a previous pharmacological study of 22Na and 36Cl transport, constitute strong evidence for the cotransport of Na, K, and Cl in rat choroid plexus.
Animals↗
Cisterna magna microdialysis of 22Na to evaluate ion transport and cerebrospinal fluid dynamics.
Microdialysis is used in vivo for measuring compounds in brain interstitial fluid. The authors describe another application of this technique to the central nervous system, namely microprobe dialysis in the cisterna magna to study the dynamics of ion transport and cerebrospinal fluid (CSF) formation in the rat. The choroid plexus is the major source of CSF, which is produced by active transport of Na from blood into the cerebral ventricles. Formation of CSF is directly proportional to the blood-to-CSF transport of Na. By injecting 22Na into the systemic circulation and quantifying its movement into CSF by microdialysis, one can reliably estimate alterations in the rate of CSF formation. The sensitivity of this system was determined by administering acetazolamide, a standard inhibitor of CSF production. Because acetazolamide is known to decrease CSF formation by 40% to 50%, the cisternal microdialysis system in animals treated with this drug should detect a corresponding decrease in the amount of 22Na dialyzed. This hypothesis is supported by the 22Na uptake curves for control versus treated animals: that is, by the acetazolamide-induced average diminution of about 45% in both the rate and extent of tracer accession to dialysate. Bumetanide, a loop diuretic, reduced by 30% the 22Na entry into dialysate. Microprobe dialysis of fluid in the cisterna magna is thus a minimally invasive and economical method for evaluating effects of drugs and hormones on the choroid plexus-CSF system.
Acetazolamide↗
Discriminative stimulus effects of psychomotor stimulants and benzodiazepines in humans.
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Dextroamphetamine↗
Discriminative stimulus effects of diazepam in humans.
Humans were trained to discriminate between 10 mg of diazepam (DZ) and placebo. Subjects reported to the laboratory in the morning several times a week for a total of 23 sessions. They filled out subjective effects questionnaires, ingested a capsule and then were free to leave. They also filled out questionnaires 1, 3 and 6 hr after leaving. During the first four sessions the drugs were identified to the subject before ingestion by letter code. During the next seven sessions the procedure was the same except the capsules were not identified to the subject. Six hours after receiving the capsule, subjects telephoned the experimenter to report their identification. When correct, they received a monetary bonus. If the identification was correct on five of the seven sessions, subjects entered the third phase. This phase had six additional training sessions as described previously. During the other six sessions that were intermixed, subjects received capsules that contained test drugs. Sixteen of 18 subjects learned the discrimination and 14 entered the third phase. They identified 2 mg of DZ, 1 mg of lorazepam and 10 mg of d-amphetamine as placebo and 2 mg of lorazepam as 10 mg of DZ. Over half of the subjects identified 5 mg of DZ and 50 mg of pentobarbital as 10 mg of DZ. DZ (10 mg) produced significant time-related changes on several subjective effect measures and these effects were typical of those produced by sedative-like drugs. The subjective effects of the test compounds were largely correlated with the drug identification. These results indicate that 10 mg of DZ can function as a discriminative stimulus in humans and this discrimination is dose-related and pharmacologically specific.
Adult↗
Three-choice discrimination among (+)-amphetamine, fenfluramine and saline in pigeons.
Five pigeons were trained to discriminate among (+)-amphetamine (AMPH; 1.7 or 3.0 mg/kg), fenfluramine (FEN; 5.6 or 10 mg/kg), and saline using a three-choice drug discrimination procedure. The results of the study demonstrated that a reliable discrimination between AMPH and FEN could be obtained and the discriminative stimulus (DS) effects of these two drugs did not overlap, i.e., were mutually exclusive. Phenmetrazine produced a dose-related increase in AMPH-appropriate responding with no responding occurring on the FEN-appropriate key. Two serotonin agonists, quipazine (5-HT2) and MK 212 (5-HT1), produced FEN-appropriate responding in two of three pigeons, while a third pigeon responded predominantly on the AMPH-appropriate key following their administration. In contrast, phencyclidine produced predominantly (greater than 50%) saline-appropriate responding, indicating that the DS effect of phencyclidine was unlike either AMPH or FEN. Finally, compounds known to have multiple DS properties such as MDA and MDMA were tested. The results with these compounds confirmed that these drugs have complex DS effects both within and across individual pigeons.
3,4-Methylenedioxyamphetamine↗
Chemistry and pharmacology of the non-benzodiazepine anxiolytic enciprazine and related compounds.
In the course of studies on tranquilizers, new non-benzodiazepine-like compounds were synthesized. These are 1-(3,4,5-trimethoxyphenoxy)-3-[4-(2-methoxyphenyl)piperazinyl]prop an-2-ol (INN: enciprazine) and derivatives thereof which were screened pharmacologically in order to evaluate their central nervous system activity. Compounds with marked antiaggressive and anxiolytic properties but without dependence potential could be detected. Enciprazine was selected for clinical investigations.
Aggression↗
Cotransport of sodium and chloride by the adult mammalian choroid plexus.
Cerebrospinal fluid formation stems primarily from the transport of Na and Cl in choroid plexus (CP). To characterize properties and modulation of choroidal transporters, we tested diuretics and other agents for ability to alter ion transport in vitro. Adult Sprague-Dawley rats were the source of CPs preincubated with drug for 20 min and then transferred to cerebrospinal fluid (CSF) medium containing 22Na or 36Cl with [3H]mannitol (extracellular correction). Complete base-line curves were established for cellular uptake of Na and Cl at 37 degrees C. The half-maximal uptake occurred at 12 s, so it was used to assess drug effects on rate of transport (nmol Na or Cl/mg CP). Bumetanide (10(-5) and 10(-4) M) decreased uptake of Na and Cl with maximal inhibition (up to 45%) at 10(-5) M. Another cotransport inhibitor, furosemide (10(-4) M), reduced transport of Na by 25% and Cl by 33%. However, acetazolamide (10(-4) M) and atriopeptin III (10(-7) M) significantly lowered uptake of Na (but not Cl), suggesting effect(s) other than on cotransport. The disulfonic stilbene 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS; 10(-4) M), known to inhibit Cl-HCO3 exchange, substantially reduced the transport of 36Cl. Bumetanide plus DIDS (both 10(-4) M) caused additive inhibition of 90% of Cl uptake, which provides strong evidence for the existence of both cotransport and antiport Cl carriers. Overall, this in vitro analysis, uncomplicated by variables of blood flow and neural tone, indicates the presence in rat CP of the cotransport of Na and Cl in addition to the established Na-H and Cl-HCO3 exchangers.
Acetazolamide↗
Na(+)-H+ exchange in choroid plexus and CSF in acute metabolic acidosis or alkalosis.
Basolateral Na(+)-H+ exchange was analyzed with an in vivo model of choroid plexus (CP) epithelium in nephrectomized adult rats anesthetized with ketamine. Acid-base balance in blood was altered for 1 h over a pH continuum of 7.19 to 7.53 by equimolar intraperitoneal injections of HCl, NH4Cl, NaCl, or NaHCO3. Compartmental analysis enabled determination of CP intracellular pH (pHi) [dimethadione (DMO) method] and the choroid cellular concentration of 23Na (stable) and 22Na (tracer). HCl acidosis reduced the outwardly directed transmembrane basolateral H+ gradient, lowered the [23Na]i by 25%, and decreased the influx coefficient (Kin) for 22Na from blood into CP parenchyma (by 45% from 0.211 to 0.117 ml.g-1.h-1) and into cerebrospinal fluid (CSF) (by 43%, from 0.897 to 0.516). Compared with acid-loaded rats (HCl or NH4Cl), the NaHCO3-alkalotic animals had significantly enhanced uptake of 22Na into the CP-CSF system. This pH-dependent transport of Na+ from blood to CP was abolished by pretreatment with amiloride, an inhibitor of Na(+)-H+ exchange. Except in severe acidosis (HCl), the choroid cell pHi (7.05 +/- 0.02 in NaCl controls) and [HCO3-] (11-12 mM) remained stable in the face of acidemic and alkalemic challenges. With respect to reaction of the blood-CSF barrier to plasma acid-base perturbations, the responses of the fourth ventricle plexus pHi, [Na+]i, and 22Na uptake were similar to corresponding ones in lateral plexuses. We conclude that in the choroidal epithelium there is a Na(+)-H+ exchange activity capable of modulating Na+ flux into the CSF by approximately 50% as arterial pH is varied from 7.2 to 7.5.
Acid-Base Equilibrium↗
Acetazolamide and insulin alter choroid plexus epithelial cell [Na+], pH, and volume.
Agents that inhibit or stimulate Na+ transport were tested for their effects on the ionic composition and volume of the in vivo choroid plexus (CP) epithelium. Ketamine-anesthetized adult Sprague-Dawley rats treated 1 h with acetazolamide or insulin were analyzed for choroid cell [Na+]i, [HCO3-]i, and pHi (dimethadione method); for transmembrane Na+ and H+ gradients; and for the kinetics of penetration of 22Na from plasma to plexus epithelium to CSF. Acetazolamide (25 mg/kg) reduced [Na+]i by 5-10 mmol/l and substantially elevated [HCO3-]i and pHi; the concurrent 22Na uptake by the in vivo choroid plexus and CSF, as quantified by the transfer coefficient, Kin (ml.g-1.h-1), was curtailed by 55-60%. Such effects on Na+ transport and distribution are likely secondary to the alkalinization of pHi induced by carbonic anhydrase inhibition. Conversely, insulin (3 U/kg ip) stimulated Na+ transport, i.e., manifested as enhanced uptake of 22Na from plasma to choroid cell and increased [Na+]i. For various treatments altering the basolateral membrane H+ gradient, the regression analysis of the 22Na Kin vs. log [H+]i/[H+]ISF (where ISF is interstitial fluid) was significant at P less than 0.01. This is consistent with effects mediated by Na(+)-H+ exchange. K+ and Cl- redistribution phenomena were coincident with altered Na+ transport, as choroidal cells retained K+, Cl-, and H2O after acetazolamide but lost K+, Cl-, and H2O with insulin treatment. A model is presented relating alterations in CP Na+ transport, KCl content, and cell volume. Overall, the findings encourage the postulate for effects of these drugs on Na+ transport basolaterally, either indirectly by attenuating [H+]i/[H+]ISF (acetazolamide) or directly by accelerating Na+ transport (insulin).
Acetazolamide↗
The evaluation of the abuse liability of drugs.
In order to place appropriate restrictions upon the availability of certain therapeutic agents to limit their abuse, it is important to assess abuse liability, an important aspect of drug safety evaluation. However, the negative consequences of restriction must also be considered. Drugs most likely to be tested are psychoactive compounds with therapeutic indications similar to known drugs of abuse. Methods include assays of pharmacological profile, drug discrimination procedures, self-administration procedures, and measures of drug-induced toxicity including evaluations of tolerance and physical dependence. Furthermore, the evaluation of toxicity using behavioural end-points is an important component of the assessment, and it is generally believed that the most valid procedure in this evaluation is the measurement of drug self-administration. However, even this method rarely predicts the extent of abuse of a specific drug. Although methods are available which appear to measure relative abuse liability, these procedures are not validated for all drug classes. Thus, additional strategies, including abuse liability studies in humans, modelled after those used with animals, must be used in order to make a more informed prediction. Although there is pressure to place restrictions on new drugs at the time of marketing, in light of the difficulty of predicting relative abuse potential, a better strategy might be to market a drug without restrictions, but require postmarketing surveillance in order to obtain more accurate information on which to base a final decision.
Animals↗
Preference for diazepam in anxious adults.
This study investigated whether anxious adults desiring treatment for their anxiety would choose to take 10 mg of diazepam (Valium) or placebo after sampling both substances under double-blind conditions. Subjective effects of the drugs were also assessed, and the relationship between self-reported subjective effects and the number of times subjects chose diazepam or placebo was examined. Fourteen male and female volunteers meeting criteria for generalized anxiety disorder were recruited. They participated in a nine-session choice experiment in which they sampled diazepam 10 mg and a placebo on the first four sessions and chose whichever they preferred on the next five sessions. Only three subjects chose diazepam on all five choice occasions, no subjects chose diazepam on three or four occasions, and 11 subjects chose diazepam on two or fewer occasions. Overall, diazepam produced typical, tranquilizer-like subjective effects. However, subjective responses to diazepam differed in the 0-2-time choosers compared with the 5-time choosers: the 0-2-time choosers showed an increase on the measure of confusion, while the 5-time choosers showed decreases on measures of anxiety and confusion and increases on measures of stimulation.
Adult↗
Stilbenes inhibit exchange of chloride between blood, choroid plexus and cerebrospinal fluid.
Disulfonic stilbenes (DIDS and SITS) were used to probe the nature of Cl transport in choroid plexus (CP) of adult rats. DIDS was more effective than SITS in reducing in vitro choroid cell [Cl]. Intravenously- or intraventricularly-administered DIDS substantially decreased 36Cl transport from blood to CP to CSF. Rate of CSF renewal was diminished nearly 30% by DIDS. These inhibitory findings implicate an anion antiporter for mediating Cl flux (and thus water) between blood and CSF.
Animals↗
Alteration of sodium transport by the choroid plexus with amiloride.
Cerebrospinal fluid (CSF) production results from active transport of Na+ from blood to CSF, which is followed by H2O and anions. Amiloride reduces Na+ movement in epithelial tissues. To ascertain if amiloride alters transport of Na+ in the choroid plexus, the drug was administered either i.p. to male Sprague-Dawley rats that were bilaterally nephrectomized to determine in vivo effects, or added to artificial CSF to incubate the choroid plexus in vitro. Choroid cell [Na+] was reduced after amiloride treatment both in vivo and in vitro. In addition, the rate of 22Na uptake into the CSF and choroid plexus (CP) was decreased after amiloride. Alterations in choroid cell [Na+] and 22Na penetration into CSF and CP occurred at relatively high doses of drug (1 mumol/ml, in vitro and 100 micrograms/g in vivo), but lower doses were less effective (0.1 mumol/ml in vitro and 10 micrograms/g in vivo). It is concluded that the effects of amiloride on Na+ distribution and transport in the CP are due to inhibition of basolateral Na+-H+ exchange.
Amiloride↗
Reinforcing and subjective effects of caffeine in normal human volunteers.
The reinforcing and subjective effects of caffeine (100 and 300 mg, PO) were determined in a group of 18 normal, healthy adults. Subjects (eight females, ten males) were light to moderate users of caffeine, and had no history of drug abuse. A discrete-trial choice procedure was used in which subjects were allowed to choose between the self-administration of color-coded capsules containing either placebo or caffeine. The number of times caffeine was chosen over placebo was used as the primary index of reinforcing efficacy. Subjective effects were measured before and several times after capsule ingestion. The low dose of caffeine was chosen on 42.6% of occasions, not significantly different from chance (50%). The high dose of caffeine was chosen on 38.9% of occasions, significantly less than expected by chance, indicating that this dose served as a punisher. Both doses of caffeine produced stimulant-like subjective effects, with aversive effects such as increased anxiety predominating after the high dose. When subjects were divided into groups of caffeine-sensitive choosers and nonchoosers, a consistent relationship emerged between caffeine choice and subjective effects; nonchoosers reported primarily aversive effects after caffeine (increased anxiety and dysphoria), whereas choosers reported stimulant and "positive" mood effects. When compared with previous findings, these results demonstrate that caffeine is less reinforcing than amphetamine and related psychomotor stimulants.
Adult↗
Assessing individual differences in ethanol preference using a cumulative dosing procedure.
Preference for ethanol versus a placebo was assessed in 12 normal volunteers usina a cumulative dosing preference test. The test consisted of four sampling sessions followed by three choice sessions. During the sampling sessions subjects received either five cumulating oral doses of ethanol (0.1 g/kg per dose) or equal volumes of placebo, at 15-min intervals. Subjective and observer-rated drug effects, psychomotor performance, drug liking ratings, and breath ethanol levels were measured at regular intervals. During choice sessions, subjects first chose which of the two substances (drug or placebo) they wished to take and ingested one unit dose. Then, at 15-min intervals throughout the session, they could ingest up to ten additional unit doses of the same substance (i.e., up to 1.1 g/kg ethanol). On average, the subjects chose the ethanol-containing beverage on 75% of the choice sessions, and they self-administered a mean total dose of 0.8 g/kg per session. Subjects varied in the amount of ethanol ingested on choice sessions, and the amount they chose was related to their subjective responses to the drug during sampling. Subjects who chose the most ethanol, whereas the subjects who chose ethanol less frequently and ingested lower doses reported primarily sedative-like effects from the drug. The results demonstrate that the cumulative dosing procedure can be used effectively to evaluate drug preferences and dose preferences in normal volunteers.
Adult↗